In 1837, Charwes Babbage was inspired by Jacqward's woom to attempt to buiwd de Anawyticaw Engine.[2]
The names of de components of de cawcuwating device were borrowed from de textiwe industry. In de textiwe industry, yarn was brought from de store to be miwwed. The device wouwd have had a "store"—memory to howd 1,000 numbers of 40 decimaw digits each. Numbers from de "store" wouwd den have den been transferred to de "miww" (anawogous to de CPU of a modern machine), for processing. It was programmed using two sets of perforated cards—one to direct de operation and de oder for de input variabwes.[2][3] However, after more dan 17,000 pounds of de British government's money, de dousands of cogged wheews and gears never fuwwy worked togeder.[4]

During a nine-monf period in 1842–43, Ada Lovewace transwated de memoir of Itawian madematician Luigi Menabrea. The memoir covered de Anawyticaw Engine. The transwation contained Note G which compwetewy detaiwed a medod for cawcuwating Bernouwwi numbers using de Anawyticaw Engine. This note is recognized by some historians as de worwd's first written computer program.[5]

The Z3 computer, invented by Konrad Zuse (1941) in Germany, was a digitaw and programmabwe computer.[9] A digitaw computer uses ewectricity as de cawcuwating component. The Z3 contained 2,400 reways to create de circuits. The circuits provided a binary, fwoating-point, nine-instruction computer. Programming de Z3 was drough a speciawwy designed keyboard and punched tape.

The Ewectronic Numericaw Integrator And Computer (Faww 1945) was a Turing compwete, generaw-purpose computer dat used 17,468 vacuum tubes to create de circuits. At its core, it was a series of Pascawines wired togeder.[10] Its 40 units weighed 30 tons, occupied 1,800 sqware feet (167 m2), and consumed $650 per hour (in 1940s currency) in ewectricity when idwe.[10] It had 20 base-10accumuwators. Programming de ENIAC took up to two monds.[10] Three function tabwes were on wheews and needed to be rowwed to fixed function panews. Function tabwes were connected to function panews using heavy bwack cabwes. Each function tabwe had 728 rotating knobs. Programming de ENIAC awso invowved setting some of de 3,000 switches. Debugging a program took a week.[10] The programmers of de ENIAC were women who were known cowwectivewy as de "ENIAC girws."[11] The ENIAC featured parawwew operations. Different sets of accumuwators couwd simuwtaneouswy work on different awgoridms. It used punched card machines for input and output, and it was controwwed wif a cwock signaw. It ran for eight years, cawcuwating hydrogen bomb parameters, predicting weader patterns, and producing firing tabwes to aim artiwwery guns.

The Manchester Baby (June 1948) was a stored-program computer.[12] Programming transitioned away from moving cabwes and setting diaws; instead, a computer program was stored in memory as numbers. Onwy dree bits of memory were avaiwabwe to store each instruction, so it was wimited to eight instructions. 32 switches were avaiwabwe for programming.

Computers manufactured untiw de 1970s had front-panew switches for programming. The computer program was written on paper for reference. An instruction was represented by a configuration of on/off settings. After setting de configuration, an execute button was pressed. This process was den repeated. Computer programs awso were manuawwy input via paper tape or punched cards. After de medium was woaded, de starting address was set via switches and de execute button pressed.[13]

Decwarative programming wanguages describe what computation shouwd be performed and not how to compute it. Decwarative programs omit de controw fwow and are considered sets of instructions. Two broad categories of decwarative wanguages are functionaw wanguages and wogicaw wanguages. The principwe behind functionaw wanguages (wike Haskeww) is to not awwow side effects, which makes it easier to reason about programs wike madematicaw functions.[17] The principwe behind wogicaw wanguages (wike Prowog) is to define de probwem to be sowved – de goaw – and weave de detaiwed sowution to de Prowog system itsewf.[18] The goaw is defined by providing a wist of subgoaws. Then each subgoaw is defined by furder providing a wist of its subgoaws, etc. If a paf of subgoaws faiws to find a sowution, den dat subgoaw is backtracked and anoder paf is systematicawwy attempted.

Compiwers are used to transwate source code from a programming wanguage into eider object code or machine code.[19] Object code needs furder processing to become machine code, and machine code consists of de centraw processing unit's native instructions, ready for execution, uh-hah-hah-hah. Compiwed computer programs are commonwy referred to as executabwes, binary images, or simpwy as binaries – a reference to de binaryfiwe format used to store de executabwe code.

Interpreters are used to execute source code from a programming wanguage wine-by-wine. The interpreter decodes each statement and performs its behavior. One advantage of interpreters is dat dey can easiwy be extended to an interactive session. The programmer is presented wif a prompt, and individuaw wines of code are typed in and performed immediatewy.

The main disadvantage of interpreters is computer programs run swower dan when compiwed. Interpreting code is swower because de interpreter must decode each statement and den perform it. However, software devewopment may be faster using an interpreter because testing is immediate when de compiwing step is omitted. Anoder disadvantage of interpreters is an interpreter must be present on de executing computer. By contrast, compiwed computer programs need no compiwer present during execution, uh-hah-hah-hah.

Just in time compiwers pre-compiwe computer programs just before execution, uh-hah-hah-hah. For exampwe, de Java virtuaw machine Hotspot contains a Just In Time Compiwer which sewectivewy compiwes Java bytecode into machine code - but onwy code which Hotspot predicts is wikewy to be used many times.

No properties of a programming wanguage reqwire it to be excwusivewy compiwed or excwusivewy interpreted. The categorization usuawwy refwects de most popuwar medod of wanguage execution, uh-hah-hah-hah. For exampwe, Java is dought of as an interpreted wanguage and C a compiwed wanguage, despite de existence of Java compiwers and C interpreters.

Typicawwy, computer programs are stored in non-vowatiwe memory untiw reqwested eider directwy or indirectwy to be executed by de computer user. Upon such a reqwest, de program is woaded into random-access memory, by a computer program cawwed an operating system, where it can be accessed directwy by de centraw processor. The centraw processor den executes ("runs") de program, instruction by instruction, untiw termination, uh-hah-hah-hah. A program in execution is cawwed a process.[20] Termination is eider by normaw sewf-termination or by error – software or hardware error.

Many operating systems support muwtitasking which enabwes many computer programs to appear to run simuwtaneouswy on one computer. Operating systems may run muwtipwe programs drough process scheduwing – a software mechanism to switch de CPU among processes often so users can interact wif each program whiwe it runs.[21] Widin hardware, modern day muwtiprocessor computers or computers wif muwticore processors may run muwtipwe programs.[22]

A computer program in execution is normawwy treated as being different from de data de program operates on, uh-hah-hah-hah. However, in some cases, dis distinction is bwurred when a computer program modifies itsewf. The modified computer program is subseqwentwy executed as part of de same program. Sewf-modifying code is possibwe for programs written in machine code, assembwy wanguage, Lisp, C, COBOL, PL/1, and Prowog.

An operating system is a computer program dat acts as an intermediary between a user of a computer and de computer hardware.
[23]

In de 1950s, de programmer, who was awso de operator, wouwd write a program and run it.[13]
After de program finished executing, de output may have been printed, or it may have been punched onto paper tape or cards for water processing.[13]
More often dan not de program did not work.
[24]
The programmer den wooked at de consowe wights and fiddwed wif de consowe switches. If wess fortunate, a memory printout was made for furder study.[24]
In de 1960s, programmers reduced de amount of wasted time by automating de operator's job.[24] A program cawwed an operating system was kept in de computer at aww times.[24]

Originawwy, operating systems were programmed in assembwy; however, modern operating systems are typicawwy written in C.

Independent of de host computer, a hardware device might have embedded firmware to controw its operation, uh-hah-hah-hah. Firmware is used when de computer program is rarewy or never expected to change, or when de program must not be wost when de power is off.[24]

Microcode programs controw some centraw processing units and some oder hardware. This code moves data between de registers, buses, aridmetic wogic units, and oder functionaw units in de CPU. Unwike conventionaw programs, microcode is not usuawwy written by, or even visibwe to, de end users of systems, and is usuawwy provided by de manufacturer, and is considered internaw to de device.